Itchy scalp? Scratching in public? And people looking askance at you? The problem could be dandruff or seborrhic dermatitis. Or worse, it could be lice.

Lice (singular: louse) are ectoparasites  that is, they live on the outside. Each insect is about the size of a sesame seed, with six legs and no wings. Human lice cannot survive on other animals such as cats, dogs and birds. They are also specific to the area they infest. They may live on the head (head lice). A slightly different variety lives in the genital area (pubic lice). A third type (body lice) lives only on the body.

School-going children are particularly likely to pick up head lice. In India, 60 per cent of girls in the age group of five to 11 are infested. This is, however, wrongly attributed to poor hygiene and low socioeconomic status. The social stigma attached to lice infestation and accusing letters from school authorities add to the psychological trauma of the child and her parents.

Lice feed on human blood and live for 30 days. If they fall off the body, they can survive on clothes, combs, crash helmets, bed sheets or pillows for two days. Each pair of lice lays about 100 eggs. These characteristics make them a tough species. They have managed to survive unchanged for more than 2,000 years. Archaeologists have found evidence of lice on Egyptian mummies, which are identical to the ones seen today.

The spread of lice occurs only if there is close contact with infested persons or their personal belongings. A louse cannot jump or fly. It has to crawl to its next victim. Once the insect has settled, it immediately starts to bite and feed. Lice release chemicals from their saliva which can cause intense scratching. This introduces bacteria to the skin which may cause secondary infection. The lymph nodes may become enlarged and appear as painful lumps in the neck.

There are many home remedies for lice. Mixtures of oils or ghee are sometimes applied in the hope that it will smother the lice. Others may shampoo frequently, thinking it will drown or wash away the insects. These, however, do not work.

The lice comb is a traditional and effective method. The comb may be made of metal, plastic or wood. Combing has to be done every day for two to three months. When the adult lice fall off, they have to be killed. Removing nits with a comb is difficult, tedious, time consuming and somewhat painful. Moreover, the child may not cooperate.

There is another effective method. Often in traditional families, all the members get their heads tonsured under some religious pretext. No hair, no lice.

Many chemicals are known to eradicate lice. Kerosene, for example, is effective when applied to the whole head and left for two or three hours. The head should be tied up securely in a cloth. But the method is dangerous as kerosene is highly inflammable.

Medicated lice treatment shampoos and lotions contain malathion, lindane and permethrin and can be applied to the hair. These chemicals paralyse the lice. The motionless insects must then be removed by washing or combing as they can recover movement in two or three hours.

The medications, however, do not remove all the lice. Only about 20 per cent are susceptible to the commonly used chemicals. The tough survivors mutate, thrive and multiply even in the presence of these chemicals. Higher concentrations offer no greater benefit. Instead, they seep through the skin and may build up to toxic levels. Also, the chemicals cannot be used in pregnant women and children under one. Treatment has to be repeated after 10 days to kill any newly hatched lice before they start to reproduce. Body and pubic lice respond poorly to lotions and shampoos.

In all the three types of lice infestation, relapse, recurrence and re-infection are common. This makes dealing with the parasite both embarrassing and frustrating.

Commercially advertised herbal products appear safer than chemicals and gullible sufferers opt for them. A few harmless ingredients like neem and tulasi are mentioned on the package. The rest are not. Their sale and production are not regulated. Their safety is questionable and side effects undocumented.

Lice can be effectively eradicated using an oral dose of 200 µgm/kg body weight of the tablet Ivermectin. It cannot be given to pregnant women or children whose weight is less than 15kg. The medicine acts only on live lice. A repeat dose is required on the eighth day when the eggs hatch.

Dr Gita Mathai is a paediatrician with a family practice at Vellore. Questions on health issues may be emailed to her at yourhealthgm@yahoo.co.in